How the Fidelius Charm works: a theory

[Amy Z]

No: HPFGUIDX 17233

Amanda wrote:

>Then how did the Weasley boys find him, when they came to rescue him
>with the car? It seems to me that everyone seems to know that Harry
>stays with his awful Muggle relatives, down to Ernie Macmillan. Of
>course, you could know where he is but still not be able to find it, 
but
>still, how did Fred, George, and Ron find him if the Dursley house is
>hidden under the Fidelius charm?

I know we've talked about this a lot before, but I had a tiny bit of a 
new (I think) thought about it.

As others have said, it seems that the FC couldn't conceal you from 
=everyone= or life would be very difficult.  The whole idea, it seems, 
is to allow you to hide only from the people you need to hide from. 

So, the FC makes you unfindable by certain people.  Who?  Surely, in 
the case of James and Lily, the DEs as well as Voldemort, for a start. 
 Perhaps everyone who has the Dark Mark, or even better, everyone 
whose loyalty is given to Voldemort whether they've been given the 
Dark Mark or not.

So what happens if someone who knows the whereabouts of someone 
protected by an FC becomes a DE afterwards?  Do they lose their 
ability to find the person?  I'd say yes.  It didn't happen with Peter 
because he was the Secret-Keeper.  But if Joe Blow down the street 
popped in to the Potters' on Wednesday and became a Voldemort follower 
on Thursday, the knowledge of their whereabouts would mysteriously 
vanish from his mind.  The charm automatically updates, as it were, to 
incorporate those who must not know.

Whaddayathink?

Amy Z

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 "Before we begin our banquet, I would like 
 to say a few words.  And here they are: 
 Nitwit! Blubber! Oddment! Tweak!"
            --HP and the Philosopher's Stone
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